< 300 mK familySample-in-vacuum 3He refrigerator - HelioxVT
The SampleProtect concept is to provide experimenters with and end-to-end method of protecting sensitive samples from accidental electrostatic discharge (ESD). The system comprises of a rack mount SampleProtect Switching Unit (SPSU) linked, via measurement grade cables and sample probes, with sample holders which include an additional socket for an equi-potential plug.
The sample holders are demountable from the probe and each probe can accommodate multiple types of sample holder. Also, sample holders are transferable between probes, or even to a HelioxVT or KelvinoxJT ULT insert.
In addition to the screened measurement cable there is a low-pass multi-stage filter can be mounted at cryogenic temperatures down to below 100mK. This has the ability to filter 24 signal lines with filter options of 4 different cut-off frequencies. The filter is constructed in an Au plated Cu chassis with RF gaskets to provide screening and thermal dumping for the filter PCB. The filter components are carefully selected surface mount components which provide very good value stability over the temperature range from ambient to sub 100mK.
During the process of mounting the sample into the sample holder, the ESD plug will be inserted. This plug links all the electrical connections to the sample together ensuring that no damaging voltages can be generated across the sample due to ESD. This plug remains in place during transport of the sample holder plus sample, meaning the sample could safely be taken from the sample preparation lab to the measurement lab, or even shipped to a lab in another continent safe from ESD damage.
When mounting the sample holder in the probe, the user keeps the ESD plug in place. Then connect the probe to the desired measurement instrumentation via the SPSU. Set the switches of the SPSU to ground all the signal lines to the desired ground, either protective ground or instrument ground. Once the switches are set correctly, remove the ESD plug from the sample holder. If appropriate for the sample the user might run some measurement checks to ensure the sample is connected and the signal train is working. Then the probe can be loaded in the cryostat and cooled to the required temperature.
Once the sample plus probe is inserted in the cryostat and the measurements are in progress, the SPSU can be used as a break-out box to switch or monitor any of the signal lines during the experiment.
The measurement cable is a carefully specified cable constructed of 13 twisted pairs, 10 pairs of 26 (19/38) AWG tinned Cu and 3 pairs of 22 (19/34) AWG tinned Cu. Each pair is individually screened with a foil screen. Each screen has external insulation to isolate it from all the other screens. Each screen also has a drain wire.
In addition, the cable has an overall foil screen which has internal insulation plus an external screen braid. The overall screen also has a drain wire. This construction facilitates overall screening with the outer screen connected to protective ground but in addition any pair can be screened to a specific measurement ground for that channel. The cross-talk increases with frequency as expected and is shown in specifications.
The PCB and LCC holders are ceramic Aluminium-Nitride (AlN) to optimise thermal conductivity.
Electrical contact plating is Ni free to minimise the remnant field effects in the sample domain.
The following sample holders are available:
PCB sample holder interface – 44 non-magnetic spring loaded pins to connect to the sample holder PCB
Three standard probes compatible with the TeslatronPT:
Each probe is available in Sample-in-Gas (SIG) or Sample-in-Vacuum (SIV) variants. The probe chassis consists of 3 thin-wall stainless-steel tubes to provide a rigid, straight, low-thermal conductivity structure and create separate electrically isolated spaces to keep measurement looms shielded from diagnostic and drive wiring.
|Temperature Range||0 to 40° C|
|Voltage rating||50 VRMS|
|Recommended Frequency Range||DC – 100 kHz|
|Mutual Capacitance||38 pF @1 kHz|
|Line Inductance||< 0.30 µH|
|Conductor DC line Resistance||< 0.18 Ω @20° C|
|Shield DC line Resistance||< 0.12 Ω @20° C|
|26AWG pairs||26AWG pairs||22AWG pairs|
|Number of twists||12 /ft (minimum)||12 /ft (minimum)|
|Temperature Range||-40 to 80°C||-40 to 80°C|
|Mutual Capacitance||30pF/ft @ 1kHz||38pF/ft @ 1kHz|
|Ground Capacitance||54pF/ft @ 1kHz||68pF/ft @ 1kHz|
|Conductor DC line Resistance||38Ω / 1000ft @ 20°C||15.5Ω / 1000ft @ 20°C|
|Shield DC line Resistance||34Ω / 1000ft @ 20°C||14.5Ω / 1000ft @ 20°C|
Cross-talk signal induced in channel 2 resulting from an excitation drive current in channel 1 plotted as a function of frequency:
Cross-talk signal induced in one conductor of a twisted pair resulting from an excitation drive current in a conductor of another twisted pair in the same cable construction, plotted as a function of frequency. Each pair is shielded with shields grounded to instrument ground:
The crosstalk measurements shown were measured on a 180cm length of cable. Cross-talk increases with frequency as expected.
The crosstalk measurements shown were measured on a 180 cm length of cable. Cross-talk increases with frequency as expected.
|Insertion loss over passband||<0.6dB||<0.6dB||<1.0dB||<1.0dB|
|Frequency rejection||-45dB @ 100kHz||-33dB @ 100kHz||-36dB @ 1MHz||-24dB @ 1MHz|
A Bode plot of filter frequency response shows the different cut-off frequency configurations: